Conventionally, stacked type secondary batteries having sheet-type electrodes stacked with an electrolyte layer interposed, and battery units formed by connecting a plurality of such stacked type secondary batteries have been known. Japanese Patent Laying-Open No. 2004-134210 describes examples of such stacked type secondary battery and battery unit.
Among the battery units described above, some are provided with a safety plug that can physically cut-off a current path. Japanese Patent Laying-Open No. 2003-346748 describes an example of the safety plug. Japanese Patent Laying-Open Nos. 2002-343331, 2004-007919 and 2004-007920 describe safety plugs for vehicle batteries.